With the proliferation of digital media and analog/digital conversion technologies, concerns of copyright-dependent organizations, especially within the music and movie industries, have significantly increased. While analog media inevitably loses quality with each copy generation and in some cases even during normal use, digital media files may be duplicated an unlimited number of times with no degradation in the quality of subsequent copies. Personal computers as household appliances, along with other portable digital media devices such as MP3 players, have made it convenient for consumers to convert media (which may or may not be copyrighted) originally in a physical/analog form or a broadcast form into a universal, digital form for location or time shifting. Furthermore, combined with the Internet and popular file sharing tools, personal computers have made unauthorized distribution of copies of copyrighted digital media much easier.
Digital rights management (DRM) technologies attempt to control use of digital media by preventing access, copying or conversion to other formats by end users, as well as controlling distribution. Various DRM systems have been employed to protect the copyrights and other intellectual property rights of digital media content creators and publishers. One such DRM system includes an encryption scheme where a key is associated with an ID number of a user's personal computer and the key only decodes the digital media when accessed from that specific computer. Other encryption schemes use limited-use encryption where a key decodes the digital media for a limited period of time. Another DRM system employs Web-based permission, where a user's computer contacts a license-verification server over the Internet to get permission, e.g., an access key, to access or play the digital media. Furthermore, some DRM systems mark the digital media with a digital watermark to prevent free distribution of the digital media content by including copyright information in the digital media as bits of information that require a special program for reading.
In addition to controlling the distribution of digital media, a need exists for techniques for embedding information into a copy of the digital media relating to a particular transaction so the digital media can be tracked.